Volcanic Eruptions Reduce Flow Of Major Rivers, New Study Shows

The Pinatubo eruption of 1991 sent aerosol particles into the air, which have since been linked to reduced regional river flow. (Photo : Wikimedia Commons )

New research from the University of Edinburgh shows that aerosol particles ejected into the air following volcanic eruptions don't just contaminate the atmosphere, they can often trigger rainfall shortages that ultimately affect river systems worldwide.

Atmospheric aerosols are tiny particles suspended in the air that reflect the heat that naturally comes from sunlight. This cools the atmosphere and leads to reduced rainfall. Specifically, volcanic aerosols form a layer in the stratosphere after major volcanic eruptions. Sulfur dioxide gas dominates the layer and is converted into sulfuric acid over the course of a week to several months after an eruption, according to NASA. Winds can spread these aerosols practically all over the world, and they can remain in the stratosphere for about two years.

To study this phenomenon, researchers analyzed flow records of 50 major rivers linked to large-scale eruptions occurring between the Krakatoa eruption in 1883 and the Pinatubo eruption in 1991.

Using this information, researchers predicted how the availability of water in regions throughout the world might be affected by future eruptions, according to a news release. Rivers were grouped by region and then computer models linked rainfall patterns with eruptions in order to predict which rivers were likely to be affected.

So what did Edinburgh researchers find?

Within a year or two of a volcanic eruption, river flows were reduced, a pattern that was found in tropical regions and northern Asia, and included the Amazon, Congo and Nile – some of the world's biggest rivers.

Conversely, river flow increased in some sub-tropical regions, including the U.S. south-west and parts of South America. Researchers linked this to the disruption of atmospheric circulation patterns.

"Our findings reveal the indirect effect that volcanoes can have on rivers, and could be very valuable in the event of a major volcanic eruption in future," Dr. Carley Iles, from the School of GeoSciences at the University of Edinburgh, said in a statement.

However, researchers are still unsure how alterations to river flow might impact human populations. The Amazon, for example, is sparsely populated, so reduced flow in this area may not have a drastic impact. But regions that are highly dependent on rivers as water sources, such as those tied to Egypt's Nile, may face more serious consequences.

The University of Edinburgh study's findings were recently published in the journal Nature Geoscience.

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